(1) Field of the Invention
The present invention relates to a developing unit for use in an image forming apparatus such as a laser printer, copier, facsimile machine etc., and in particular relates to a technology for replenishing, as required, the developing hopper as a part of a developing unit, with the toner for image development.
(2) Description of the Prior Art
An image forming apparatus such as a laser printer, copier, facsimile machine, etc., utilizing the electrophotographic technique, has an image forming portion for forming a desired image on a sheet for recording. In this image forming portion, the surface of a photosensitive member as an image bearer is uniformly electrified with charge of a particular polarity and then is illuminated with an optical image so as to form a static latent image corresponding to the image. For the purpose of visualizing this static latent image, the image forming portion includes a developing unit and other components. The developing unit is configured of a developer hopper holding a developer and having a developing roller etc., for supplying the developer to the developing position where the developing roller opposes the photosensitive member. Further, since the toner in the developing hopper is consumed, a toner replenishing device for replenishing the developing hopper with the toner as necessary is arranged adjacent to the developing hopper, thus configuring the developing unit.
In a developing unit of the above type, if the toner reserve container for replenishing the developing hopper with the developer is arranged on the top, the developing unit would be bulky as to its height so a waste space would arise inside the image forming apparatus, thus making the whole image forming apparatus bulky. For this reason, the toner reserve container is horizontally arranged adjacent to the developing hopper to reduce the height of the developing unit, thus making the developing unit into a thinned configuration and hence making it possible to configure a compact image forming apparatus as a whole by eliminating the unnecessary space which would arise inside the image forming apparatus.
An example of such a developing unit is disclosed in Japanese Patent Application Laid-Open Sho 63 No.213877. In this developing unit, the toner reserve container is arranged at the side of the developing hopper and has a conveying element that conveys and agitates the toner inside the toner reserve container so that the conveying element feeds (supplies) the toner into the toner replenishing portion from which the toner is supplied to the developing hopper.
Japanese Patent Application Laid-Open Hei 10 No.123815 has proposed a developing unit having a toner replenishing device having a simpler configuration compared to the developing unit disclosed in the aforementioned publication. This developing unit 60 comprises, as shown in FIG. 1, a developing hopper 61 which incorporates an agitating roller 62 for agitating the developer stored in developing hopper 61 and a developing roller 63 for conveying the developer to the developing area that opposes the photosensitive member. Further, a toner reserve container 64 is horizontally arranged at the side of developing hopper 61. Toner reserve container 64 stores toner 69 for replenishment and incorporates an agitator 65 that agitates and conveys the stored toner 69.
Formed between developing hopper 61 and toner reserve container 64 is a toner supply opening 66, at which a toner replenishing roller 67 made up of sponge etc., for replenishing the toner into developing hopper 61 with the toner is positioned. The agitator 65 is rotated in the direction of the arrow in the drawing during toner replenishment so as to feed the toner to replenishing roller 67 whilst agitating the toner stored in toner reserve container 64.
Agitator 65 is configured of rotational, agitating vanes (a pair of plates arranged on both sides) with a conveying sheet 68 of a flexible sheet-like element, attached at one, end of the vanes. Accordingly, as agitator 65 is turned, conveyer sheet 68 scoops up the toner 69 accumulated or stored at the bottom of toner reserve container 64 whilst agitating it and collects the toner thereover to feed it to replenishing roller 67. During this, the toner 69 over the sheet is supplied to replenishing roller 67 by making use of the force of action that causes conveying sheet 68 to restore itself due to its own flexibility.
In a developing unit of this kind, toner reserve container 64 is arranged at the side, and agitator 65 etc., are provided in the toner reserve container 64, whereby toner 69 in toner reserve container 64 can be conveyed completely to toner replenishing roller 67. Thus, the toner storage volume can be increased by enlarging the developing unit horizontally while the height of the developing unit can be suppressed.
In the developing units shown in FIG. 1, since toner reserve container 64 is horizontally arranged at the side of developing hopper 61, there is no increase in height. However, if the toner storage volume of toner reserve container 64 is further increased, the height cannot but increase.
If toner reserve container 64 is enlarged only in the horizontal direction in order to increase the toner storage volume, agitator 65 shown in FIG. 1 cannot agitate and convey the toner well enough. That is, if the distance of conveying sheet 68 from the fixed end to the distal end is set long enough to convey the toner in the vertical direction, it is difficult to secure good enough performances of agitation and conveyance of the toner in the left and right, or lateral direction. As a result, the toner inside toner reserve container 64 cannot be completely used and a certain toner will remain unused. Further, the remaining toner is not agitated and hence the toner gathers into a mass in the stationary area of the toner reserve container 64, which may then be fed into the agitable area by some reason such as vibration etc. for instance, and hence the aggregation may be fed to replenishing roller 67. When such a toner aggregation is fed to developing hopper 61, it may cause development failures, or other deficiencies.
For these reasons, in the apparatus disclosed in Japanese Patent Application Laid-Open Hei 10 No.123815, the rotary shaft 65a of agitator 65 is set off-centered closer to the developing hopper 61 side while conveying sheet 68 when it is positioned horizontally is formed long enough so that its front end reaches the right side wall (rear wall) of toner reserve container 64 in FIG. 1, whereby toner supply can be stabilized while securing a desired amount of toner for replenishment and eliminating toner stagnation. In FIG. 1, a reference numeral 71 designates a regulating element for limiting the developer adhering to developing roller 63 to the predetermined amount and 72 designates a concentration detector for detecting the toner concentration of the developer in developing hopper 61.
Here, in accordance with the toner replenishing device having a configuration shown in FIG. 1, toner 69 in toner reserve container 64 is adapted to be scooped up and fed to the replenishing portion from above to replenishing roller 67. In contrast to this, those disclosed in Japanese Patent Application Laid-Open Hei 6 No.236110 and Japanese Patent Application Laid-Open Hei 7 No.271163 are configured so that the toner in the toner reserve container is scooped up and fed from below (underhand configurations). In these cases where the toner is fed in such a manner, the rotary shaft of the agitator needs to be positioned above the replenishing portion so that the configuration inevitably tends to be greater in height.
Here, in the developing unit thus configured shown in FIG. 1, the toner reserve container 64 is configured so that its dimensions or its volume can be made as large as possible in order to reduce the frequency of charging the toner to toner reserve container 64. Therefore, toner reserve container 64 should become greater proportionally with the increase of the stored amount of the toner. In order to suppress the increase in height, toner reserve container 64 is enlarged in the lateral direction in the figure. Conversely, in order to suppress the increase in size of the lateral direction, the depth or the size in the vertical direction should be enlarged. Anyway, the volume of toner reserve container 64 should be enlarged.
Therefore, in the toner replenishing device configured as shown in FIG. 1, in order to agitate the whole toner 69 stored in toner reserve container 64 as uniformly as possible and feed it to developing hopper as efficiently as possible, it is necessary to convey the toner to replenishing roller 67 in a high enough amount. For this reason, conveying sheet 68 attached to agitator 65 is provided so as to be elongated as much as possible. In other words, the distance of conveying sheet 68 from its attached position with agitator 65 to its distal end is adapted to be long.
Contrary to expectation, if conveying sheet 68 is formed to be long, the agitating and conveying performances lower because of difficulties in securing the rigidity of conveying sheet 68. This conveying sheet 68 is made up of a flexible material. The conveying sheet is formed of polyethylene terephthalate (PET) film etc., for example so as to have good flexibility and have a tolerance against deformation and curving.
Particularly, as the toner is conveyed by the rotation of agitator 65, conveying sheet 68 becomes curved and deformed repeatedly, so that the sheet may become plastically deformed and bent, unable to reset its curvature and deformation and hence lose its conveying performance and its toner agitating performance. For example, conveying sheet 68 may be plastically deformed, becoming bent at the part joined to the attachment edge of agitator 65 in FIG. 1 and failing to recover its original shape.
In most cases, conveying sheet 68 becomes bent and the plastically deformed portion becomes whitened. The whitening is the phenomenon that the portion having had loads applied thereto is caused to plastically deform and the properties, performance, mechanical characteristics etc. of the part become lowered, not reaching breakdown or rupture but the damaged portion becomes wrinkled forming into a cloudy white compared to the background color of the surrounding resin. This causes lowering of conveyance and agitation due to deformation of the conveying sheet.
In view of the above problems, it is an object of the present invention to provide a developing unit equipped with a toner replenishing device wherein the toner in the toner reserve container can be sufficiently fed and brought to the toner replenishing portion with an improved conveying performance.
It is a particular object of the present invention to provide a developing unit equipped with a toner replenishing device wherein toner conveyance can be secured for a long period of time by reducing deformation of the conveying sheet and preventing its elastic breakdown etc., with a simple structure and stable toner replenishment is ensured especially when a large toner reserve container is used.
The developing unit equipped with a toner replenishing device in accordance with the first invention to achieve the above object is a developing unit equipped with a toner replenishing device which has a toner reserve container for supplying the toner to a developing hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developing hopper, including: a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; and a conveying sheet of a flexible material attached to the rotator for scooping up the toner stored in the toner reserve container and conveying the toner into the replenishing portion and being characterized in that the conveying sheet is bent in the rotational direction of the rotator at a halfway point thereof with a predetermined angle a, forming a bent portion.
For example, as shown in FIG. 5, the conveying sheet (58) is bent at a halfway point with an angle a forming a bent portion (58a). When the rotator (57) rotates and the conveying sheet becomes deformed as it comes into sliding contact with the inner wall of the toner reserve container, the deformation is relieved around the position of bent portion 58a so as to inhibits the conveying sheet from being greatly deformed at the attachment edge d of the rotator. As a result, no plastic deformation or the like of the conveying sheet will occur at the attachment edge d, thus making it possible to maintain the necessary stable toner conveyance for a long period. In the conventional configuration, when the rotator rotates and the conveying sheet is deformed as shown in FIG. 6, the part of the conveying sheet joined to the attachment edge d of the rotator is deformed greatly. Repeated stress acting on this area causes the sheet to be plastically deformed, so the toner conveyance tends to lower gradually. In the present configuration, however, stresses arising in the conveying sheet can be relieved around the bent portion provided at a halfway point to thereby prevent such plastic deformation.
Next, in the apparatus having the configuration of the first invention, the same operation effect can be obtained if the bent portion is formed in a curving shape. Since the bent portion is formed of a curving structure instead of an angled configuration, a longer life can be expected.
Further, in the apparatus having the configuration of the first invention, setting the angle a at the bent portion within the range from 90xc2x0 to 170xc2x0 assures sufficient toner conveyance and can prevent plastic deformation as stated above, thus making it possible to maintain stable conveyance in the long term.
In the unit having the configuration of the first invention, h is set at a value within the range of (H/4)xe2x89xa6hxe2x89xa6(2H/3), where H is the distance from the attached position of the conveying sheet with the rotator to the bottom of toner reserve container and h is the distance from the position of the bent portion of the conveying sheet to the attachment edge of the rotator. Therefore, the bent portion can be positioned within the appropriate range related to the dimensions of the toner reserve container. In this way, the bent portion is specified appropriately based on the capacity and size of the toner reserve container, or the stored amount of the toner, beyond mere provision of the bent portion, so that it is possible to maintain a more stabilized conveyance.
Moreover, in the apparatus having the configuration of the first invention, h is set at a value within the range of 20txe2x89xa6hxe2x89xa6100t, where t is the thickness of the conveying sheet and h is the distance from the position of the bent portion of the conveying sheet to the attachment edge of the rotator. Therefore, it is possible to specify the size of the bent portion appropriately relative to the thickness of the conveying sheet. In particular, since the bent portion is set closer to the attached portion of the conveying sheet with the rotator when the conveying sheet is thin whereas the bent portion is set distant from the attached portion of the conveying sheet with the rotator when the conveying sheet is thick, it is possible to effectively prevent plastic deformation of the conveying sheet and hence maintain its stable conveying function.
The apparatus of the second invention to achieve the above object is a developing unit equipped with a toner replenishing device which has a toner reserve container for supplying the toner to a developing hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developing hopper, including: a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; and a conveying sheet of a flexible material attached to the rotator for scooping up the toner stored in the toner reserve container and conveying the toner into the replenishing portion and being characterized in that the conveying sheet is composed of a fixed portion for attachment to the rotator and a conveying portion for scooping up and conveying the toner on the free end side, having a thickness smaller than that of the fixed portion.
In other words, the fixed portion for fixing the conveying sheet to the rotator is made thicker while the conveying portion connected thereto and in charge of toner conveyance is made thinner. Therefore, even if the conveying sheet deforms greatly when scooping and conveying the toner, the thinner part, i.e., the conveying portion only deforms greatly. Thus, similar to the above first invention, the deformation can be absorbed by the conveying portion, so that plastic deformation of the fixed portion at the attachment edge of rotator can be effectively prevented. Moreover, since the fixed portion of the conveying sheet is formed to be thick, it is possible to effectively perform toner agitation and conveyance while providing sufficient rigidity of the conveying sheet.
In the apparatus having the configuration of the second invention, the fixed portion and conveying portion having different thicknesses and constituting the conveying sheet can be formed by integral molding or by lamination. Particularly, use of the injection molding process facilitates fabrication of an integrated conveying sheet having a stepped configuration. Alternatively, lamination of multiple sheets facilitates fabrication of a conveying sheet having a stepped configuration. For example, the conveying sheet may be formed in a simple manner by laminating and joining one or two sheets of film having a necessary thickness to one or both sides of a sheet of film having the same thickness. Thereby, it is possible to prevent plastic deformation of the fixed portion being attached to the rotator, and hence maintain stable toner conveyance for a long time.
In the apparatus having the configuration of the second invention, h is set at a value within the range of (H/4)xe2x89xa6hxe2x89xa6(2H/3), where his the distance from the position at which the thickness of the conveying sheet changes between the fixed portion and the conveying portion to the attachment edge of the rotator and H is the distance from the attached position of the fixed portion with the rotator to the bottom of toner reserve container. This setting enables the conveying sheet to be configured in accordance with the toner storage capacity of the toner reserve container and to provide stable toner conveyance for a long period, thus making it possible to enhance the effect of preventing plastic deformation.
The apparatus of the third invention to achieve the above object is a developing unit equipped with a toner replenishing device which has a toner reserve container for supplying the toner to a developing hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developing hopper, including: a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; a conveying sheet of a flexible material attached to the rotator for scooping up the toner stored in the toner reserve container and conveying the toner into the replenishing portion; and a reinforcing element arranged protectively in the rotational direction of the rotator and attached to the rotator and being characterized in that the conveying sheet is attached to the rotator via the reinforcing element.
In accordance with this invention, the conveying sheet, especially its rigidity, is reinforced by the reinforcing element. Therefore, a high enough toner conveyance can maintained. Further, since the conveying sheet is inhibited by the reinforcing element from being bent greatly, so that no reduction in toner conveyance occurs due to plastic deformation and hence it is possible to keep stable toner conveyance for a long period. Therefore, it is possible to use the conveying sheet in the long term.
In the apparatus having the configuration of the third invention, the conveying sheet is bonded to the reinforcing element at an area corresponding to the area where the reinforcing is attached to the rotator and the other part of the conveying sheet is unbonded with respect to the reinforcing element. Accordingly, the deformation of the conveying sheet is constrained greatly by the reinforcing element so that the conveying sheet is deformed greatly but plastic deformation at that portion can be inhibited. With the deformation of the conveying sheet constrained by a reinforcing element, the conveying sheet will be deformed at the area where no reinforce element is present by the loads from the inner face of the toner reserve container and from the toner and the deformation cannot be absorbed so that the stresses may concentrate on that portion, possibly causing plastic deformation. However, the conveying sheet is not bonded in whole area of the reinforcing element, so that the deformation due to the loads is dispersed and hence there is no fear of plastic deformation occurring.
Next, in the apparatus having the configuration of the third invention, when the reinforcing element is formed of a material thicker than the conveying sheet, this configuration naturally, reinforces the conveying sheet and hence gives high enough rigidity to the conveying sheet, to thereby enhance the toner conveyance.
In the apparatus having the configuration of the third invention, when the reinforcing element has a bent or curved portion at the distal end thereof, it is possible to enhance the reinforcing effect of the reinforcing element and hence improve the toner conveyance. When the conveying sheet is deformed by the loads from the inner surface of the toner reserve container and the toner, the conveying sheet being deformed is supported by the distal part of the reinforcing element, which causes concentrated deformation on the distal part. Therefore, the reinforcing element would give way losing its rigidity. However, because the reinforcing element of this configuration has a bent or curved portion at the distal part, this reinforcing element is able to secure its rigidity and functions to provide rigidity to the conveying sheet and hence provides high enough toner conveyance function.
In the apparatus having the configuration of the third invention, when the reinforcing element is greater in thickness or longer in projected amount in the areas corresponding to both extremes of the conveying sheet than in the area corresponding to the central area of the conveying sheet, it is possible to maintain the toner conveyance at the both extremes of the conveying sheet so that the distribution of the amount of toner conveyance can be made approximately uniform with respect to the longitudinal direction of the conveying sheet. Particularly, when the conveying sheet deforms, it tends to deform to a higher degree in both extremes than in the central part. Therefore, the reinforcing element is longer in projected amount or greater in or thickness in the both extremes than in the central part, to enhance the reinforcement on the conveying sheet at both extremes. Thereby, it is possible to make the conveying performance approximately uniform across the full range.
In the apparatus having the configuration of the third invention, when the width (W) of the bent or curved portion at the distal end of the reinforcing element is made greater in the areas corresponding to both extremes of the conveying sheet than in the area corresponding to the central area of the conveying sheet, it is possible to make the toner conveying performance approximately uniform across the length of the conveying sheet.
In the apparatus having the configuration of the third invention, when the reinforcing element is formed with a corrugated structure having a section of a continuous semicircular, trapezoidal, sinusoidal or other concavo-convex series, it is possible to further enhance the reinforcing effect. In this case, if the reinforcing element is equal in thickness to, or thinner than, the conveying sheet, it is possible to provide high enough reinforcing effect and hence secure high enough toner conveyance.
In the apparatus having the configuration of the third invention, similarly to the above first and second inventions, as to the projected amount of the reinforcing element, h is set at a value within the range of (H/4)xe2x89xa6hxe2x89xa6(2H/3), where h is the projected amount of the reinforcing element and H is the distance from the attached position of the fixed portion with the rotator to the bottom of toner reserve container. This setting assures the toner conveyance and enables stable toner conveyance even if the conveying sheet is used in the long term.
Next, the apparatus of the fourth invention to achieve the above object is a developing unit equipped with a toner replenishing device which has a toner reserve container for supplying the toner to a developing hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developing hopper, including: a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; and a conveying sheet of a flexible material attached to the rotator for scooping up the toner stored in the toner reserve container and conveying the toner into the replenishing portion and being characterized in that the conveying sheet has a tapered configuration such that the thickness becomes gradually thinner from the position attached to the rotator toward the free end side which performs toner conveyance.
Illustratively, the conveying sheet is thick at the portion to be attached to the rotator and gradually becomes thinner or tapered as it approach to the distal end for conveying the toner. Therefore, it is possible to inhibit plastic deformation of the fixed part of the conveyance sheet joined to the rotator, whereby toner conveyance can be continuously kept for a long time. Similarly to the second invention, though the conveying sheet deforms at its distal part that scoops and conveys the toner, plastic deformation at the attached end portion with the rotator can be inhibited.
In the apparatus according to the first through fourth inventions, when the conveying sheet to be attached to the rotator is integrally molded, there is no risk of the sheet being peeled off, so that it is possible to keep more stabilized conveyance compared the case where the conveying sheet is bonded and fixed to the rotated. Further, the positioning of the conveying sheet to the rotator can be improved in accuracy, which makes it possible to provide more stabilized toner conveyance. In this case, owing to recent advances in the field of injection molding, use of an injection molding technique makes it possible to perform integral molding of the rotator and conveying sheet using two different materials. Therefore, when the integral molding is produced by selecting the most suitable materials for the rotator and conveying sheet, respectively, it is possible to provide a configuration which has the advantages described heretofore and presents full functions and realize improved toner agitation and conveyance. In particular, the distal end part of the conveying sheet or the part which comes in sliding contact with the inner wall surface of the toner reserve container, can be formed with a material excellent in slidability, where by a further beneficial effect can be expected.